Celebrity private eye Bo Dietl has had a regular eight-top table at the restaurant every Thursday night since 1977. Page Six reported last week how New York City banker Christopher Bond dropped $6,000 at a charity auction to use Dietl’s table for one night, but has had trouble claiming his prize.

Bond says he initially arranged a July date, only to have Dietl cancel on him eight days out. He then tried for Nov. 5, but Dietl’s assistant said it wasn’t available. A verbal sparring match between the two men ensued that ended with Bond threatening to just show up at Rao’s and Dietl telling him that if he did, he’d punch Bond in the face.

So what is it about the tiny Italian restaurant in East Harlem that has grown men putting up their dukes? Though the place first opened in 1896, it wasn’t until charismatic owner Frank Pellegrino took the reins in the ’70s that Rao’s morphed into one of the city’s most legendary spots.

Back then, East 114th Street wasn’t the safest of areas, but the fact that members of the Gambino, Genovese and Lucchese crime families were allegedy regulars allowed patrons to park their cars out front without fear.

Bo Dietl seen outside Rao’s.Christopher Sadowski

In 1977, after a three-star review in the New York Times lead to an avalanche of reservation requests, Pellegrino began a unique system of time-sharing his restaurant’s four tables and six booths. Customers are appointed real estate on regular nights — some weekly, some monthly — and many of the earliest regulars, like Dietl, still retain those seats. (Dietl’s table is known as “the Earth” because it’s the biggest in the house, seating eight to 10 people.)

“Every table has been booked every night for the past 38 years,” Pellegrino told Town & Country in early 2015. “No one gives them up. In every three-month period, I see all my clients, and now I’m dealing with their children and grandchildren.”

If a table owner can’t use his table or booth one night, it’s their responsibility to find a friend to take it or to let Pellegrino know well in advance. Owners don’t dare sell their tables unless the funds go to charity. “If Frankie found out [someone sold a spot], he’d go crazy,’’ says a source.

The room is full of colorful characters, like bartender Nicky the Vest, so known for his assortment of 50 or so stylish waistcoats (some of which are said to light up). At one point, Pellegrino earned the nickname “Frankie No” because of how many times he’s had to tell aspiring patrons “no.”

Indeed, for mere mortals looking to dine at the restaurant, it’s next to impossible. Calling Rao’s yields a message saying the place is booked through the year, no matter when you call.

Rao’s has only 10 tables plus a cozy “house table” for pals of owner Frank Pellegrino, who walks the floor singing songs like “My Girl” and “My Way.”Post Staff Composite

There’s a small bar for walk-ins, but it doesn’t serve food. It’s said that some smooth talkers have managed to land the “house table” for two — the only two-top, and the only table without an “owner” in the room — after hanging out at the bar and charming Pellegrino.

Rumor has it that some crime family members may still be regulars, though the wiseguy quotient is allegedly much lower than it was years ago. Pellegrino’s tailor is a regular, as is “Goodfellas” actor Johnny Williams (aka Johnny Roastbeef).

Rao’s owner Frank Pellegrino.Eilon Paz

But mostly those who own tables tend to be old-school power brokers, like billionaire CEO Ron Perelman and former Sony Music head Tommy Mottola, who took Mariah Carey there when she was just 18. ESPN sportscaster Dick Schaap reportedly had a table until his death in 2001 — it now belongs to his family, as reservations are allowed to be passed down.

When Martin Scorsese visited in the late ’80s with actors Ray Liotta and Lorraine Bracco, he wound up casting 21 people from Rao’s as extras in “Goodfellas.”

“Angelina Jolie and Denzel Washington had dinner with me, and Andre Agassi used to have meatballs with me all the time,’’ Dietl tells The Post. “And [while he was filming] ‘The Wolf of Wall Street,’ Leo DiCaprio came to Rao’s with me, and they even shot part of the film there.’’ In fact, the scene included Dietl himself, advising embattled hedge funder Jordan Belfort (DiCaprio) to get a lawyer and not to speak to the FBI on his own.

Bo Dietl and Leonardo DiCaprio at Rao’s.

The traditional southern Italian fare — fusilli with sausage and marinara; veal stuffed with mozzarella and prosciutto — is OK or great, depending on who you ask, though it’s expensive by anyone’s standards. No credit cards are accepted. “You have to bring a roll of hundreds,” says a source. The table’s host generally disappears with the waiter into a private room to settle the bill.

Food critic Gael Greene recalls, “A few years ago, I was invited by Susan Kasen [who has a table on Mondays]. I saw Bill Gates and his wife with Warren Buffett at a back table. Frank [Pellegrino] went over to the jukebox and played Sinatra singing ‘My Way,’ then asked everyone to join in. Gates and Buffett did with great enthusiasm. That was a wonderful moment.”

“Everybody in the room is an interesting character,” Charles Koppelman, the former chairman of Martha Stewart Living Omnimedia and current CEO of CAK Entertainment, tells The Post. “You can have the head of the Stock Exchange and someone who is a recently convicted felon.”

Though the restaurant keeps the names of its regulars — and where they sit — under wraps, The Post has found out that these boldfacers “own” tables.​

Steve Witkoff: Real-estate investor and partner in Le Bilboquet.

Charles Koppelman: CEO of CAK Entertainment, has a booth.

Susan Kasen: Owns the Vineyard at Strawberry Ridge — and a Monday table.

Sonny Grosso: Film producer and ex cop who inspired “The French Connection.”